The present invention relates to an image projection apparatus such as a liquid crystal projector, and more particularly to an air exhausting structure of the image projection apparatus.
The image projection apparatus (hereinafter referred to as projector) has an air exhausting structure which forcibly exhausts air that has cooled a light source lamp or other heat generating devices (or exothermic devices) to the outside with a fan. However, when the projector is used in a state in which an exhaust air outlet of the projector is placed near an obstacle such as a wall (that is, in a state in which the exhaust air outlet is blocked), the cooling of the heat generating devices is obstructed, and this may cause trouble in the operation of the projector. Therefore, many projectors include a temperature sensor thereinside and have a protection function to warn a user or to turn off the light source lamp when an abnormal temperature increase is detected.
Japanese Patent Laid-Open No. 2002-258238 discloses a projector in which plural temperature sensors are provided thereinside to monitor the temperatures of respective portions inside the projector. Further, Japanese Patent Laid-Open No. 2003-043577 discloses a projector which includes a temperature sensor for detecting the temperature of an external air and another temperature sensor for detecting the temperature in the vicinity of the light source lamp, and turns off the light source lamp when the difference between the temperatures detected by these temperature sensors becomes large.
However, when the projectors disclosed in aforementioned Japanese Patent Laid-Open Nos. 2002-258238 and 2003-043577 are used in the state in which the exhaust air outlet is blocked, the temperature of the air around the light source lamp initially increases. Afterwards, a lamp case which is a heat insulating member surrounding the light source lamp is heated, and then a temperature increase is detected by the temperature sensor after the heat transmits to the air around the lamp case from it. In other words, the temperature increase of the light source lamp is detected after the heat transmits to the lamp case and the air therearound, so that the state in which the exhaust air outlet is blocked cannot be detected quickly.
A temperature sensor may be provided inside the lamp case. However, the temperature inside of the lamp case increases even under a normal usage condition. Therefore, a mechanical sensor using a bimetal is commonly used as the temperature sensor provided inside of lamp case. Furthermore, the mechanical sensor is used to forcibly turn off the light source lamp for final protection thereof, and it is not easy for a user to recover the projector from the state in which the mechanical sensor has been activated.